Description

We report on the lasing characteristics of three- and five-stack InAs∕GaAsquantum dot(QD) lasers grown by metal organic chemical vapor deposition. By increasing the number of stacked dot layers to 5, lasing was achieved from the ground state at 1135nm for device lengths as short as 1.5mm (no reflectivity coatings). The unamplified spontaneous emission and Z ratio as a function of injection current were also investigated. While the five-stack QD lasers behaved as expected with Z ratios of ≈2...[Show more] prior to lasing, the three-stack QD lasers, which lased from the excited state, exhibited Z-ratio values as high as 4. A simple model was developed and indicated that high Z ratios can be generated by three nonradiative recombination pathways: (i) high monomolecular recombination within the wetting layer, (ii) Auger recombination involving carriers within the QDs (“unmixed” Auger), and (iii) Auger recombination involving both the QD and wetting layer states (“mixed” Auger), which dominate once the excited and wetting layer states become populated.